1. Field of the Invention
The present invention relates to a method for driving a plasma display panel, and more particularly to a method for driving a plasma display panel which provides an AC (Alternating Current) discharge type display.
2. Related Art
In general, a plasma display panel (hereinafter, abbreviated as PDP) has a number of features including thin structure, flicker-free, large display contrast ratio, comparatively large screen, high response speed, spontaneous light emitting type, possible multiple color light emission by use of phosphors. For this reason, they have come into wide use in recent years in the field of displays for computers and color image displays and the like. PDPs can be classified according to operating principle into an AC type, having dielectric-covered electrodes and operate by indirect AC discharge, and DC type, in which the electrodes are exposed in the discharge space and which operates by DC discharge. AC types can be further classified into a memory operating type that uses a memory of the discharge cell as a drive method, and a refresh-type that does not use this memory. The intensity of a PDP is proportional to the number of discharges, that is, to the number of pulse voltage repetitions. With respect to the above refresh type, when a display capacity increases, the luminescence is lowered. Thus, such a PDP is mainly used as a PDP with its small display capacity.
FIG. 1 is a schematic perspective view illustrating a configuration of one display cell of a conventional AC memory operation type PDP. This display cell is made up of two glass insulation substrates 1 and 2, at the rear and front, respectively, a scanning electrode 3 and a sustaining electrode 4, with trace electrodes 5 and 6 superposed thereover for the purpose of reducing the electrode resistance, a data electrode 7 formed on the insulation substrate 1 so as to perpendicularly cross the canning electrode 3 and the sustaining electrode 4, a discharge gas space 8, filled with a discharge gas that is helium, neon, or xenon, or a mixture thereof, in the space between the insulation substrates 1 and 2, a bulkhead wall 9 for the purpose of establishing the discharge gas space 8 and partitioning the display cell, a phosphor 11 for converting the ultraviolet light generated by a discharge in the discharge gas to a visible light 10, a dielectric film 12 covering the scanning electrode 3 and the sustaining electrode 4, a protective layer 13 made of magnesium oxide or the like, which protects the dielectric film 12 from electrical discharge, and a dielectric electrode 14 covering the data electrode 7.
FIG. 2 of the accompanying drawings shows in schematic form the electrode placement in an AC-type plasma display panel. The scanning electrodes S and the sustaining electrodes C are each mutually parallel, and the data electrodes D perpendicularly cross the scanning electrodes S and the sustaining electrodes C to form the cells that emit light. One cell is formed by one scanning electrode, one sustaining electrode, and one data electrode. The number of cells over an entire screen is therefore the product n×m, where n is the number of scanning electrodes and m is the number of data electrodes.
The drive operation of a PDP configured as noted above is described below, with reference made to FIG. 3 of the accompanying drawings.
Time period 1 of FIG. 3 is a priming period, during which a priming pulse Ppr-s is applied to the scanning electrodes and a waveform thereof is a saw toothed pulse, and a priming pulse Ppr-c is applied to the sustaining electrodes, and a waveform thereof is a rectangular waveform. During the priming period, the positive polarity saw toothed pulse applied to the scanning electrodes and the negative polarity rectangular pulse applied to the sustaining electrodes generate a priming discharge in the discharge space between the scanning electrodes and the sustaining electrodes of all cells, activated particles are generated that facilitate the generation of cell discharge, simultaneously with which negative and positive wall charges become attached over the scanning electrodes and the sustaining electrodes, respectively.
The discharge in the above-noted case is a weak discharge performed at a point at which the potential difference between surface discharge electrodes exceeds the discharge triggering voltage. Period 2 is a priming erasing period, during which a priming erasing pulse Ppe-s for reducing the wall charges that had become attached to the scanning electrodes and the sustaining electrodes during the priming period is applied to the scanning electrodes, the waveform thereof being a gradually falling negative waveform. Period 3 is a scanning period, during which a negative polarity scanning pulse Psc applied to the scanning electrodes and a positive polarity data pulse Pd applied to the data electrodes pause a writing discharge, thereby generated wall charges become attached to the cells at locations at which light is to be emitted in a subsequent sustaining period. This writing discharge during a scanning period is only generated at the intersection of a scanning electrode to which the scan pulse Psc is applied and a data electrode to which the data pulse Pd is applied.
When a discharge occurs, a wall charge becomes attached to the scanning electrodes and the sustaining electrodes. In contrast to this, a cell in which discharge did not occur has no wall charge attached thereto. Period 4 is a sustaining period, during which positive sustaining pulses Psus-s and Psus-c are applied to the scanning electrodes and the sustaining electrodes alternately, starting at the sustaining electrodes. In doing this, a wall charge becomes attached to a cell selectively written during the scanning period, a positive sustaining pulse voltage and the wall charge voltage being weighted to each other, so that a potential difference between electrodes exceeds a minimum discharge voltage, thereby a discharge occurs. Once the discharge is generated, a wall charge is disposed so as to cancel the voltage applied to each electrode. Therefore, a negative charge is accumulated on the sustaining electrodes C, and a positive charge is accumulated on the scan electrodes S.
In the next sustaining pulse, a positive voltage pulse is applied to the scan electrodes S, and weighting relevant to a wall charge is generated in the scan electrodes S, a potential difference between the electrodes exceeds a minimum discharge voltage, and a discharge is generated. Then, in the sustaining period, the sustaining pulses Psus-c and Psus-s are repeatedly applied, thereby the light emission of a selected display cells is sustained. On the other hand, because the wall charge at a cell at which a writing discharge did not occur is extremely small, even if a sustaining pulse is applied, no sustaining discharge occurs. Period 5 is a sustaining erasing period, during which a sustaining erasing pulse Pe-s is applied so as to reduce the wall charge that had become attached to the scanning electrodes and the sustaining electrodes during the sustaining period, the waveform thereof being a gradually falling negative waveform at the scanning electrode side. The five periods of priming, priming erasing, scanning, sustaining, and sustaining erasing are collectively referred to as a sub-field.
As noted above, because the priming discharge is performed over the entire screen, however, there is a slightly noticeable light emitted from cells which are not driven, thereby resulting in a lowering of the contrast relative to the non-display portions. It is possible to reduce the emitted light intensity (priming intensity) during priming by lowering the priming voltage. FIG. 4 shows the relationship between the priming intensity and the priming voltage. If the final voltage that the priming voltage reaches is lowered for the purpose of reducing the priming intensity, however, this will lead to an increase in the data voltage. FIG. 5 shows the relationship between the priming voltage and the data voltage. If the priming voltage is decreased, therefore, it is necessary to increase the data voltage, and there are cases in which there are problems such as an increase in the power consumption and an increase in the cost of the driver IC (Integrated Circuit).
Because the data voltage must be increased as the screen load increases, if the priming voltage is lowered, when the screen load becomes large there are the problems of insufficient data voltage to cause a writing discharge, and an increase in the cost of the driver IC.
Accordingly, it is an object of the present invention to provide a drive method and drive circuit for a plasma display panel which enables a reduction in the priming intensity without causing an increase in the data voltage.